Global state synchronization failure between JavaScript window and Python namespace

State Synchronization Behavior

There is no automatic, bidirectional synchronization mechanism between the Python global namespace and the JavaScript window object in PyScript/Pyodide. The two environments operate in isolated memory spaces; while Pyodide provides a proxy layer to access JavaScript objects, it does not mirror state changes in real-time across the language boundary.

Confirmed Technical Behavior

• One-Way Proxying: When you access js.window from Python, you are interacting with a proxy. Assigning a value to a property on that proxy updates the JavaScript object immediately.
• Namespace Isolation: Updating js.window.myVar does not automatically create or update a Python variable named myVar in the Python global scope.
• Asynchronous Drift: Because PyScript execution is subject to the browser's event loop, Python code reading from the window object during an asynchronous callback will see the current JS value, but any local Python cached versions of that state will be stale.

Implementation Strategy for Reliable State

To ensure state consistency, you must treat the JavaScript window object as the single source of truth and avoid duplicating that state within Python variables. Use the following pattern:

import js

# WRONG: Creating a local Python copy that will drift
# state_val = js.window.appState

# RIGHT: Always access the proxy directly
def get_state():
    return js.window.appState

def set_state(new_val):
    js.window.appState = new_val

If your application requires Python to react immediately to changes made by JavaScript (outside of Python-triggered events), you must implement a manual observer pattern or a callback system, as the runtime does not support native data binding between the two namespaces.

Verification Steps

1. JS Verification: Open the browser console and type window.yourVariableName to confirm the value was actually set by Python.
2. Python Verification: Print js.window.yourVariableName immediately before the logic gate where the state is required to ensure you are not reading a cached local variable.

Diagnostic Detail Needed: Are you attempting to synchronize complex Python objects (classes/dicts) or simple primitives (strings/ints)? Complex objects require explicit conversion via to_js() to avoid proxy-related reference errors.